Process of manufacturing photographic silver halide emulsions and products obtained thereby



Patented June 12, 1928 UNITED STATES PATENT oFFic s.

OTTO MATTHIES, OF DESSAU, PETER WULFF, F STARNBERG, AND WALTER DIETEELEAND BRUNO WENDT, OF DESSAU, GERMANY, ASSIGNOES TO I. G. FARBENINDUSTRIEAKTIEN'GESELLSCHAFT, OF FRANKFORT, GERMANY.

PROCESS OF IMANUFACTURING PHOTOGRAPHIC SILVER HALIDE EMULSION'S ANDPRODUCTS OBTAINED THEREBY.

No Drawing. Application filed 311137 19, 1926, Serial No. 121,781, andin Germany July 25, 1925.

It is known that sulphydric acid or sul phides produce more or less fogin hotographic silver halide emulsions. Alt ough attempts have been madeto add only very minute, exactlydefined, quantities of these chemicalcompositions, they generally are found to produce fog, although acertain increase in the sensitivity of the emulsion may be perceived atthe same time.

The sensitivity of photographic silver halide emulsions ma be raisedwithout fogging, according to t e present invention, by adding to theemulsion, during emulsion making, small quantities of salts soluble inwater, the anions of which contain at least three atoms of sulphur. Theaddition may be made to the constituents of the emulsion, or at any stepof emulsion making, or to the finished emulsion. 2a The compoundsadapted to be added for this purpose, e. g. sodium trithionate, sodiumtetrathionate, the sodium salt of the trithiodi-glycolic acid(COOH.OH,.S.S.S.CH .COOH) produce the desired effect in emulsions havingan alkaline reaction, as well as in neutral and weakly acid emulsions.With silverions they form silver-compositions which so are diflicultlysoluble in water and decom-' pose spontaneously producing asilver-metalloid-composition.

The decomposable silver-sulphur-compounds having been formed in thesilver halide crystals formerly free from sulphur,

or on their surfaces, the. decomposition producing silver-metalloidtakes place in the emulsion. The invention depends on the knowledge thatthe sensitivity of photo- 40 graphic emulsions is raised in aparticularly good manner when traces of silver-metalloid, especially ofsilver sulphide,constituting reducing agents,--are produced by the de- Acom osition of the above-mentioned decomposa le compounds inside of thesilver halide crystals or on their surfaces. The use of solublesulphides or of colloidal silver sulhide solutions never resultsinanalogous increases in the sensitivity of the halide emulsions.

Selenium and tellurium are equivalent tobe raised.

Example 1.

To a photographic silver halide emulsion prepare from 1 kg. of gelatineand 4.00 g. of silver nitrate, there is added 50-100 mg. of sodiumtrithionate. By this addition the sensitivity increases from 12 to 17Scheiner.

y Example 2. The same effect is reached by substituting for; the sodiumtrithionate in Example 1,

30-40 mg. of the sodium salt of the trithiodi-glycolic acid.

Example 3.

' To the emulsion manufactured according to Example 1, there is added,instead of sodium trithionate, 5 com. of a n TO solution of potassiumselenotrithionate which is obtained by dissolving selenium in-potassiumsul hite.

aving now particularly described andascertained the nature of ourinvention and in what manner it is to be performed, we declare that Whatwe claim is:

1. Process of making a photographic silver halide emulsion whichcomprises ,incorporating in said emulsion a water-soluble salt theanions of which contain at least three atoms of an element of thesulphur g in; 2. rocess of manufacturing photographic silver halideemulsions which comprises addin to the emulsion Water-soluble saltstheanions of which contain at least three atoms of an element of thesulphur group.

elatine, particles of silver halide suspended t erein, and a smallamount of a water-solu- 15 Me compound the anions of which contain atleast three atoms of sulphur.

7. Photographic layers comprising the silver halide emulsion defined inclaim 6.

In testimony whereof we aflix our signa- 90 ture s.

OTTO MATTHIES.

WALTER DIETERLE. PETER WULFF.

BRUNO WENDT.

